This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. A positive Toluidine blue (TBO) stain has been used clinically as an indicator of oral neoplasia for many decades. Clinical visualization of the stain is used as a subjective evaluator of lesion presence and delineation. Preliminary studies have demonstrated that a positive TBO stain can be mapped accurately and quantified in 3-D at tissue surface and subsurface using in vivo multiphoton microscopy (MPM) . Subsequent selective photodestruction of the stained tissues using Photodynamic Therapy (PDT) may also be possible. However, the precise localization and potential binding sites of TBO within the tissues remain unknown. This information is foundational if TBO is to be used for high-resolution diagnosis and selective PDT.